Method of manufacturing panels and panel so produced



United States Patent 2,987,431 METHOD OF MANUFACTURING PANELS AND PANEL S0 PRODUCED Franz Biichler, Gossau, Switzerland No Drawing. Filed Aug. 30, 1957, Ser. No. 681,165 Claims priority, application Switzerland Aug. 31, 1956 1 Claim. (Cl. 154-121) The present invention relates to a method of manufac turing panels, in particular for covering walls, tables etc.

One of the features characterizing this invention is that a panel produced according to the method possesses excellent mechanical properties, a high degree of resistance to scratching and a large measure of resistance against impacts and chemical influences. A further advantageous feature is that the subsequent formation of hair line cracks in the panel surface is positively eliminated.

Another feature is the high degree of heat resistance of such a panel so that, by way of example, hot pots and pans will not damage the panel.

A further feature of the invention is that the panel size is not determined by the printable width of paper webs but any size panel may be manufactured as desired.

Yet a further feature is that novel color effects so far unknown can be obtained.

A final feature is that no discoloration will in the finished panel occur owing to local heat action and that formation of air bubbles in the panel during and after manufacture is eliminated.

Covering panels for walls and the like have so far been manufactured by applying various colored synthetic resin varnish coats on a base sheet such as wood fiber sheets, asbestos-cement sheets (Eternit sheets), and preferably applying a colorless synthetic varnish finish at the end as by spraying. Application of these synthetic baking varnishes is usually performed by means of filling knives and spray guns or automatic spraying units. The various synthetic varnish coats are baked in two or three cycles in hot-air stoves or by means of infra-red rays. Recently so-called polyester varnishes have been employed for certain applications instead of synthetic baking varnishes. These panel surface finishes usually possess a low degree of chemical stability and, above all, the mechanical resistance to abrasion and to scratching as well as heat resistance are unsatisfactory. On table leaves so treated, smoldering cigarettes for instance leave permanent burning marks.

A further known method of manufacturing panels employs several paper sheets impregnated with synthetic resins as laminates, which are pressed. The base sheet usually consists of phenolic resin impregnated kraft paper; the paper sheet of the central layer is either in plain color or printed with different designs, while the top sheet is translucent. This method, however, displays the disadvantage. that the printed papers available therefor are costly and obtainable in a limited range in respect of colors, designs and, in particular, sizes. Moreover these panels of a thickness of only approximately 1.5 mm. as such are not rigid enough and must therefore be cemented to a rigid base.

Covering panels are also manufactured in which the base sheet consists of a wood fibre sheet pressed together with printed and impregnated paper sheets. The drawbacks of these panels are the same as those cited in connection with the above process, with the exception that rigidity is improved.

In addition, all such known coveringpanels display the disadvantage that their resistance against extended local application of heat is too low. If a pan containing smok ing oil is left to stand on a kitchen table topped with this material, heating may cause bubbles to appear between the individual sheet layers and possibly at the bonding seam between the panel and the base sheet. In the majority of cases, the printed paper will become discolored as well.

Another disadvantage of some known covering panels now marketed consists in the danger of subsequent formation of hairline cracks in the surface owing to climatic influences. Such damage is partly attributable to a lack of adhesive strength of the protective film on the underlying layer, partly to tensions built up in the finished panel. It has been attempted to eliminate such damage by adding paper fibers to the translucent protective film. Incorporation of glass fibers ground together with the resin has also been proposed, but it was only partly successful and caused difiiculties in application as well as a large amount of scrap without completely eliminating the known disadvantages.

The method of manufacturing panels according to the present invention is characterized by the fact that at least one coat of a synthetic resin varnish is applied to a base sheet and subsequently baked, whereupon the base sheet so treated is warm pressed with a synthetic resin impregnated sheet to obtain thorough setting down to the base sheet and to form a translucent non-cracking protective coat.

The panel manufactured according to this method is also part of the present invention.

As used in the present specification, the term synthetic resin varnish designates a pigmented synthetic resin solution of glycerophthalates, aminoplasts or a mixture of the two substances.

The method according to this invention will now be described in detail:

A synthetic resin varnish paint is sprayed on a base sheet with the desired design, such as by a spray-gun, if necessary in two or more coats. This paint is then baked into the base in a stove and the base so treated pressed together with a sheet impregnated with melamine resin, e.g. a paper sheet, at an elevated temperature. This sheet, which is termed warm pressed layer below, after such treatment forms a protective coat which is translucent so that the colors and designs of the baked paint coats are perfectly visible and which possesses a surface sutficiently hard for the mechanical strength to meet all desirable requirements, i.e. that it is completely resistant to scratching, impacts of hard objects, contact with burning cigarettes and the like. The formation of bubbles between the individual layers, and discoloration is entirely impossible even when the product is subjected to the action of heat for some time.

The base material may consist of solid sheets made of wood fibers, wood splinters, glass fibers, synthetic materials, cellulose and even sheet metal. The synthetic resin paints employed are mainly alkyd resins, urea resins or a combination of the two materials, which may also be compounded with melamine resin. These synthetic resin paints may be sprayed on the base, rolled on or applied by a doctor (screen printing). Baking of these materials into the base sheet may be effected by either convection furnaces, by infra-red radiation or electric high-frequency energy. The sheet forming the translucent protective coating may consist of paper fibers, textile fibers, glass fibers or even of mineral fibers and it may be impregnated not only with melamine but also with thermosetting synthetic resins.

A precautionary measure against the formation of cracks may comprise the incorporation of, translucent fillers'oflamellar structure, such as finely powdered mica, fillers. of; fibrous form being dispensed. with; Surface.- active fillers such as silica gel have also yielded satisfactory results. It has further been found that the danger of cracking owing to tensions in the top layer is substantially reduced if the color and design carrying layer con- Example N0. 1

A synthetic varnish paint which is a pigmented synthetic resin solution of glycerophthalates and aminoplasts is applied, as by a spray gun, to form a primer on a base plate formed of asbestos fibers, which has previously been roughened by means of a grinder and emery paper. This synthetic resin varnish paint is then baked for approximately 45 minutes in a hot-air stove at a temperature of about 140 C. After this process, the sheet so treated is ground in order to remove the rough fibers which may be upstanding on the one hand,'and to obtain the uniformly rough and porous surface required for the next operation. In the second operation, the base so treated is passed through the automatic spraying machine on a conveyer belt, in which machine several spray guns arranged consecutively again apply synthetic resin paint at small air pressures such as .4 gauge atmosphere. In order to obtain the desired design, these spray guns are movably arranged and are automatically and continuously displaced according to the design required. This synthetic resin paint may be pigmented with another color in each spray-gun so that the desired design is obtained by superimposing the paint droplets of various colors on one another. The base sheet so treated is then again passed through the baking stove and baked at l40150 C. during approximately one hour. Afterwards the sheet is placed in a conditioning unit until it has obtained a hygroscopic moisture of approx. 7 or 8 percent. After conditioning, the sheet is again ground as after the first baking process, or roughened. by means of grinding brushes. The base sheet so treated is then pressed together with a sheet impregnated with melamine resin and pumice powder, eg, a paper sheet, at a temperature of 150 C. and a pressure of 100 k-g./cm. during 20 minutes, and subsequently cooled. The pressed sheet used, of which the surface condition also. produces the surface structure of the finished panel manufactured, may have a mirror polish, or it may be dull or grained. Under the action of pressure and heat, the melamine resin is forced through the porous baked synthetic resin varnish paint layers during the pressing operation and reaches the base sheet which it connects with the baked synthetic resin paint with appropriate additions into an integral, crack-resistant unit. thus forms a protective film which is entirely translucent on the one hand so that, the colors and design of the baked paint layers are perfectly 'visible, and on the other hand it possesses a surface which is so hard that its mechanical strength fully meets all desirable requirements, i.e. that it is completely unaffected by scratching, impacts of hard objects and against contact with burning cigarettes and the like. Moreover, the formation of bubbles between the individual layers and discoloration is eliminated even when the product is subjected to the action of heat for extended periods, owing to the complete setting which eliminates air inclusions. For particular applications, eg. for the electrical industry, a phenol resin impregnated kraft paper sheet may be pressed to the underside of the base sheet.

Example N0. 2

The warm-pressed layer so pressed 4 of the synthetic resin component as a filler designed to roughen the surface. The roughening eifect so obtained increases the surface and improves the adhesive strength. In this case, the varnish surface need not be treated by grinding.

4 Example N 0. 3 Here again, the procedure is as in, Examples 1 or 2. The synthetic resin solution required for the warmpressed layer is, however, compounded with 5 to 25 percent by weight commercial mica powder (e.g. mica) and ground in a ball mill prior to impregnating the paper sheet.

Example N 0. 4

Corresponds to Example No. 3 with the exception that the synthetic resin solution required for the warm-pressed layer is compounded with silica gel in quantities of 5 to 30 percent by weight of the synthetic resin component, and ground in a ball mill.

Example No. 5

In the preparation of the warm-pressed layer, the latter is subjected to a pretreatment (impregnation) with sorbitol, which fills the capillaries of the sheet fibers (paper, textile, glass, mineral) before resin impregnation so that the fibers can resist the tensile stresses after being pressed.

Panels so manufactured can, in particular, be employed to cover walls or to improve a table top and the like. If the base material is sutficiently strong, i.e. thick, they may also be used as table tops without reinforcement, which are equipped with only a frame and the necessary legs.

Various changes and modifications may be made in the method described herein without departing from the true scope and spirit of this invention, and it is intended that such obvious changes and modifications be embraced by the annexed claims. I

Having now particularly described and ascertained the nature of my said invention and in what manner the same is to be performed, I declare that what I claim is:

A method of manufacturing a panel, comprising the steps of applying on a fibre board forming a base plate a layer of a pigmented solution of synthetic resin formed of glycerophthalates and aminoplasts and containing a filler in an amount of from 10-50 percent by weight of said resin to roughen the surface of said base plate, said layer forming the decorative coat, baking said layer, then covering said layer with a cover sheet impregnated with a melamine resin compounded with 525 percent by weight of the resin component mica powder, applying heat and pressure to the cover sheet to bond the sheet and the layer together to form a translucent protective film with the synthetic resin of said cover sheet being forced through said layer of synethetic resin.

References Cited in the file of this patent UNITED STATES PATENTS OTHER REFERENCES r Halls: Fillers for Pasties, Plastics (British )','October 1942, pages 352-353. 

